Machine for comminuting materials

ABSTRACT

A machine for comminuting material by impact, comprising a hollow impeller rotatable about a substantially vertical axis, an upwardly opening material inlet and radially outward material outlet ducts (40). The ducts (40) are sufficiently narrow to prevent material striking the walls thereof with a high impact force. A plurality of anvils are arranged to be struck by material which has emerged from the ducts (40). One side wall of each duct (40) is lined with a tile (55) of a ceramic material such as aluminum oxide.

This invention relates to a machine for comminuting materials.

GB-A-2092916 describes a machine for comminuting materials which is inthe form of an impact breaker, that is to say, a machine for comminutingbrittle materials by the dissipation of kinetic energy impact. Themachine described in GB-A-2092916 comprises a hollow impeller rotatableabout substantially vertical axis and having interior walls, an upwardlyopening material inlet and at least one radially outward materialoutlet. Means are provided for feeding the material to be comminutedinto the material inlet, the feeding means comprising an upperstationary portion and a lower portion which is rotatable to impart tothe material being fed an angular velocity about an axis substantiallycoincident with the axis of rotation of the impeller. The feeding meansis so dimensioned as to cause material fed therethrough to be in achoked condition when the lower portion is rotating. At least one anvilis arranged to be struck by material which has emerged from the materialoutlet or outlets after travelling along at least a portion of theinterior walls of the impeller.

As the material to be comminuted travels through the radially outwardmaterial outlet or outlets, the walls thereof are subject to wear, and,accordingly, those walls are lined with materials which are abrasionresistant. This abrasion resistant material is provided in the form ofremovable components which can be replaced as and when excessive wearhas occurred. The replacement of these wear parts can constitute a verysignificant portion of the cost of operating the impact breaker,depending on the nature of the material being comminuted, besides whichit is inconvenient to have to stop the machine frequently to change thewear parts. It is therefore desirable to be able to use for these wearparts materials having the highest abrasion resistance possible.

From the point of view of resistance to abrasion the best materialscurrently available are certain ceramics. Setting aside some, forexample tungsten carbide, which are extremely expensive, the most usefulmaterials as regards abrasion resistance include aluminium oxide andsilicon carbide. However, these materials are very brittle, and cantherefore only be used where the maximum impact force to which they areliable to be subjected is sufficiently low not to cause them tofracture. It is an object of the present invention to provide a machinefor comminuting material by impact, the design of which is such thatbrittle materials can be used for the wear parts mentioned above.

According to the present invention there is provided a machine forcomminuting material by impact, comprising a hollow impeller rotatableabout a substantially vertical axis an upwardly opening material inletand at least one radially outward material outlet duct, the or each saidduct being sufficiently narrow to prevent material striking the wallsthereof with a high impact force; and at least one anvil arranged to bestruck by material which has emerged from the said at least one duct.

An embodiment of the present invention is shown in the accompanyingdrawings, in which:

FIG. 1 is a plan view of an impeller forming part of the machineaccording to the present invention;

FIG. 2 is a section taken along line A--A in FIG. 1, on a larger scale;

FIG. 3 is a section taken on line B--B in FIG. 1, also on a largerscale;

FIG. 4a and 4b are a plan view, and a section on line A--A in FIG. 4arespectively, of an accelerator plate forming part of the impeller ofFIG. 1;

FIG. 5 is an underplan view of a rotatable ring forming part of themachine according to the present invention;

FIG. 6 is a plan view of a wear part carrier forming part of the machineaccording to the present invention; and

FIG. 7 is a diagrammatic view of part of what is shown in FIG. 1, withvarious dimensions indicated, with reference to which the dimensions ofthe impeller are discussed below.

The impeller illustrated in the drawings is rotated about its verticalaxis, and material to be comminuted is fed into the impeller from above,i.e. in the direction of the arrow shown in FIG. 3. The material is fedinto the impeller through a feed tube (not shown) the external diameterof which is just less than the internal diameter of the first impellercomponent which the material encounters, namely a ring 10. The innerperipheral wall 11 of the ring 10 is partially obscured by thedownstream end portion of the feed tube. The feed tube is arranged to beaxially adjustable with respect to the ring 10, so that the extent towhich the peripheral wall 11 is exposed to the material be fed into theimpeller can be adjusted. This enables the feed conditions to beadjusted to suit the material concerned. The feed tube and ring 10cooperate to provide a condition of choked feed, a condition which isexplained in more detail in GB-A-2092916. As can be seen from FIG. 5,the ring 10 has on its lower surface six regions 12 of generallytriangular shape where the surface is hardened. The reason for thepresence of the regions 12 is explained below.

Material entering the impeller has some angular momentum imparted to itby the ring 10. It then falls onto an accelerator plate 20 which has thegeneral shape of a shallow, upwardly pointing cone, with a cone angle ofabout 140°. In the illustrated embodiment the accelerator plate 20 has avertically extending rib 21 running diametrically across it. Dependingon the type of material to be comminuted this rib may or may not beprovided. For example, in the case of material which enters the impellerin the form of large diameter lumps it is preferable for the rib 21 tobe absent. As seen in plan view (FIG. 4a) the accelerator plate 20 hassix generally triangular projections 22 spaced about its circumference.The accelerator plate 20 rests on a base plate 30 which forms the lowerend of the impeller.

The outer annular region of the impeller defines a plurality of ducts40, in this case six such ducts, through which material is impelled bythe accelerator plate 20 in a radially outward direction. An annulararray of stationary anvils is disposed around the outside of theimpeller, and material passes radially outwardly through the ducts andstrikes the anvils at high speed, thus comminuting the material. Thearray of anvils can be of basically conventional form, and is thereforenot shown further here.

The ducts 40 are defined in part by six wear part carriers 50, one ofwhich is shown in plan view in FIG. 6. Each wear part carrier 50 isapproximately arcuate in plan view, with a curved radially outer wall 51a straight side wall 52 and a third wall 53 which defines a recess 54 inwhich is received a rectangular tile 55 of a ceramic material such asaluminium oxide. The walls 51,52 and 53 are interconnected by atransverse web 56 which can be seen most clearly in FIG. 2. Extendingfrom top to bottom of the wear part carrier, through the web 56, arethree cylindrical shafts 57a, 57b and 57c. As will be explained below,the shaft 57c is needed on only two out of the six wear part carriers,but for convenience of manufacture all wear part carriers are made ofthe same construction and hence all include the three shafts.

The outer surface of each ceramic tile 55 defines one side wall of arespective duct 40. The opposite side wall is provided by the outer faceof the straight wall 52 of an adjacent wear part carrier. The top wallof each duct 40 is provided by a ceramic tile 58 of a material such asaluminium oxide, one edge of which rests on a respective tile 55 and theother edge of which rests in a recess 59 provided in the upper edge ofthe wall 52 of a respective wear part carrier. The tiles 58 arerectangular, and this leaves approximately triangle portions of theupper wall of each duct at its radially inner end to be provided by theunderside of the ring 10. It is for this reason that the hardenedportions 12 are provided, since it is these portions which are actuallyexposed to the interior of the ducts.

The bottom wall of each duct is provided by the upper surface of aceramic tile 60. One edge of each tile 60 is located below the edge of arespective tile 55, and the other edge of each tile 60 is received in arecess 61 in the wall 52 of a wear part carrier, the recess 61 beinglocated directly below the recess 52.

An annular cover ring 70 is mounted on the top of the impeller and apair of bolts 71a and 71b pass through the shafts 57a and 57brespectively of each wear part carrier 50, the lower end of each boltbeing received in a threaded bore 72 in the baseplate 30. In addition,two clamp plates 73 are provided, the radially inner end of each clampplate extending over an edge portion of the ring 20 and the radiallyouter portion of each clamp plate having an aperture 74 through whichpasses a bolt which then passes through the cylindrical shaft 57c of thewear part carrier below it, through the baseplate 30 and into aturntable (not shown) on which the impeller is mounted for rotation. Theturntable is driven by a suitable motor, for example a diesel engine oran electric motor. The bolts 71a and 71b and the bolts which pass theapertures 74 ensure between them that the impeller rotates with the turntable as a unit, i.e. that is no relative rotation between the variouscomponents. The ceramic tiles 55 are held in their respective recesses54 by an adhesive applied to the rear face. The tiles 58 and 60 may besimilarly adhered to the cover plate 70 and base plate 30. However, suchadhesive is not essential and one can rely simply on the fact that thesetiles are trapped in place by the surrounding components.

Before proceeding to further consideration of the way in which thepresent invention operates one further constructional feature which maybe mentioned here is that in each of the wear part carriers 50 the outersurface of the curved wall 50 is provided over a region adjacent itsjunction with the straight wall 52 with a wear-resistant face portionwhich is denoted by 51a. The reason for this is that comminuted materialmay build up in the region between the impeller and the anvils and thatas the impeller rotates it may, in effect, have to cut through thisbuilt up comminuted material. The region which bears the brunt of thiscutting out action is the region 51a.

Some characteristics of the operation of the present invention will nowbe described with reference to FIG. 7 which shows diagrammatically twoof the six ducts 40. Some of the dimensions are indicated on the drawingby references a to e.

In FIG. 7:

O is the center of rotation of the impeller;

X is an arrow representing the direction of rotation of the impeller;

Y are arrows representing the directions in which material leaves theducts;

a is the distance by which the wall 52 (defining the side of the ductwhich the forward wall as considered with reference to the direction ofrotation of the impeller) extends beyond the tile 55 (defining the otherside of the duct);

b is the width of the duct;

c is the length of the wall 52 minus a;

d is the diameter of the impeller measured to the radially outer end ofthe wall 52; and

e is the radial distance from 0 to the radially inner end of the wall52.

In a particular embodiment, d is 600 mm.

Consider by way of example a piece of material to be comminuted whichtravels radially outwardly from the center of rotation O of the impellertowards one of the ducts with a constant radial velocity. If oneconsiders the movement of the piece of material from the point of viewof the frame of reference of the duct, i.e. one treats the duct asstationary and only the material as moving, it will be apparent that thepiece of material must move towards the tile 55 along a curved pathwhich is at least approximately that of a parabola. The range of angleswithin which the piece of material can strike the tile plate 55 dependson the values of the parameters a to e. In particular, the narrower theduct is made the more oblique is the maximum angle at which the piece ofmaterial can strike the tile 55, i.e. the further from an angle normalto the tile. This reduces the effect of the impact of the materialagainst the tile and thus reduces the likelihood of the tile fracturing.Also, the narrower the duct the nearer to the radially inner end of theduct must the piece of material strike the tile. The linear velocity ofthe tile is of course lowest at its radially inner end, which means thatthe velocity of impact between the piece of material and the tile islowest if the material strikes the wear plate near the radially innerend. This too helps to reduce the risk of fracture.

The following table sets out the presently preferred ranges of variousratios of the various parameters a to e. These values relate to the useof a ceramic tile 55 made of 95% density aluminium oxide formed by coldpressing and sintering. The significance of the parameter a is thatthere is a risk of material bouncing back from the anvils and hittingthe ceramic tiles. The presence of a substantial value for provides, ineffect, a shield to reduce the likelihood of this happening.

It is to be understood that although the top and bottom walls of theducts are also subject to a certain amount of wear, and for this reasonare lined with ceramic tiles, the amount of wear there is significantlyless than the wear to which the tile 55 is subjected. The side wall ofeach duct opposite its respective tile 55 is not particularlysignificant and no ceramic lining is required. It is sufficient that thewall should be of a reasonably abrasion resistant metal.

                  TABLE                                                           ______________________________________                                        Ratio           Max    min.                                                   ______________________________________                                        a/b             0.67   0.4                                                    b/d             0.5     0.167                                                 c/d             1.0    0.34                                                   e/d             0.45   0.34                                                   ______________________________________                                    

I claim:
 1. A machine for cominuting material by impact, comprising:ahollow impeller rotatable about a substantially vertical axis; anupwardly opening material inlet and at least one radially outwardmaterial outlet duct; and at least one anvil arranged to be struck bymaterial which has emerged from said duct; said duct being defined by apair of side walls, a bottom wall and a top wall, and wherein at leastthe side wall which is rearward, as considered in the direction ofrotation of the impeller, has a surface provided by a wear resistanttile, and the top and bottom duct walls each having a surface providedby respective wear resistant tiles, at least the wear resistant tileused for the rearward side wall being of ceramic material, said ductbeing sufficiently narrow to prevent material striking the side wallsthereof with a high impact force.
 2. A machine according to claim 1,wherein the ceramic material is selected from aluminium oxide andsilicon carbide.
 3. A machine according to claim 1, wherein a pluralityof ducts is present, and the impeller comprises a plurality of carriersarranged in an annular array around the impeller, with each duct havingone side wall thereof provided by a one carrier and the other side wallthereof provided by an adjacent carrier.
 4. A machine according to claim3, wherein each carrier has a wear-resistant surface portion adjacentthe radially outer end of the forward side wall, as considered in thedirection of rotation of the impeller.
 5. A machine according to claim1, wherein the value of b/d, where b is the width of the duct and d isthe radius of the impeller measured to the radially outer end of theduct is from 0.167 and 0.5.
 6. A machine according to claim 1, whereinthe value of e/d, where e is the radial distance from the center ofrotation of the impeller to the radially inner end of the duct and d isthe radius of the impeller measured to the radially outer end of theduct, is from 0.34 to 0.45.
 7. A machine according to claim 1, whereinthe value of a/b, where a is the distance by which the forward wall ofthe duct extends beyond the rearward wall and b is the width of theduct, is from 0.4 to 0.67.
 8. A machine according to claim 1, whereinthe value of c/d, wherein c is the length of the side wall of the ductminus a, a being the distance by which the forward wall of the ductextends beyond the rearward wall, and d is the radius of the impellermeasured to the radially outer end of the duct, is from 0.34 to 1.0.